scispace - formally typeset

Journal ArticleDOI

Optical anisotropy of aligned pentacene molecules on a rubbed polymer corresponding to the electrical anisotropy

01 Jan 2010-Current Applied Physics (North-Holland)-Vol. 10, Iss: 1, pp 64-67

AbstractWe report on the optical anisotropy of a pentacene film on a rubbed (poly)vinylalcohol (PVA) layer related to the electrical performances of the pentacene organic field effect transistors (OFETs) depending on the direction of a current flow. The optical anisotropies of the PVA films are negligible with respect to whether or not rubbing process. In the pentacene OFET on the rubbed PVA layer, however, the optical anisotropy is observed and the anisotropy of the electrical performances directly corresponds to the optical anisotropy of the pentacene thin-film on the rubbed PVA layer.

Topics: Pentacene (57%), Anisotropy (53%), Organic field-effect transistor (51%)

...read more

Content maybe subject to copyright    Report

Citations
More filters

Journal ArticleDOI
Abstract: A novel method of strain-aligning polymer films is introduced and applied to regioregular poly(3-hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge-mobility anisotropy, where the in-plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two-dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane-on and edge-on packing configurations, as the strain alignment is found to induce a significant face-on orientation of the originally highly edge-on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge-mobility anisotropy of 9, providing a simple and effective method to investigate charge-transport mechanisms in polymer semiconductors.

252 citations



Journal ArticleDOI
Abstract: Zinc oxide (ZnO) thin films were prepared on glass substrate by sol–gel dip-coating method. The paper presents the properties of zinc oxide thin films deposited on soda-lime-glass substrate via dip-coating technique, using zinc acetate dehydrate and ethanol as raw materials. The effect of withdrawal speed on the crystalline structure, surface morphology and optical properties of the thin films has been investigated using XRD, SEM and UV–Vis spectrophotometer. X-ray diffraction study shows that all the films have hexagonal wurtzite structure with preferred orientation in (0 0 2) direction and transmission spectra showed highly transparent films with band gap ranging from 3.78 to 3.48 eV.

26 citations


Journal ArticleDOI
Abstract: We systematically studied how the mobility in a pentacene thin-film transistor (TFT) with an anisotropic polymeric insulator is decisively dependent on the deposition rate of pentacene molecules. This occurs from the view point of both the morphological coverage and optical phase retardation. Until a value of 2 A/s, as the deposition rate increases, the alignment of pentacene molecules, examined by optical retardation improves due to the guaranteed diffusion process for more stable positioning and an improved packing density at an early stage. The corresponding mobility is found to be proportional to the deposition rate in this regime. For increased deposition rates above 2 A/s, due to the shortage of diffusion processing time, evaporating pentacene molecules damage the pre-deposited and pre-aligned pentacene molecules on the anisotropic insulator. Thus, the optical retardation starts to decrease definitely when the early stage packing density is saturated. The resultant mobility is found to be inversely proportional to the deposition rate. Based on the morphological, optical results and the corresponding mobility, we confirm that the deposition rate of an organic semiconductor has a critical effect on the structural orientation, the molecular growth, and the resultant mobility in organic TFTs.

13 citations


Cites background or methods from "Optical anisotropy of aligned penta..."

  • ...Recently, the alignment of pentacene molecules along the rubbed direction of polymers was reported [8,9,22]....

    [...]

  • ...In order to determine the optical anisotropy, which represents the degree of alignment capability, a photoelastic modulator (PEM) (Hinds, PEM-90) was used [22]....

    [...]

  • ...In order to generate the anisotropic property, a rubbing process for the PVA layer was conducted by a commercial rubbing machine with a cotton velvet material at a roller speed of 500 rpm [22]....

    [...]

  • ...In addition, the PEM method was recently introduced as a new technique to examine the aligning features of pentacene molecules [22]....

    [...]


Journal ArticleDOI
Abstract: We report on the enhancement of the field-effect mobility of solution-processed 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) by unidirectional topography (UT) of an inkjet-printed polymer insulator. The UT leads to anisotropic spreading and drying of the TIPS-pentacene droplet and enables to spontaneously develop the ordered structures during the solvent evaporation. The mobility of the UT-dictated TIPS-pentacene film (0.202 ± 0.012 cm2/Vs) is found to increase by more than a factor of two compared to that of the isotropic case (0.090 ± 0.032 cm2/Vs). The structural arrangement of the TIPS-pentacene molecules in relation to the mobility enhancement is described within an anisotropic wetting formalism. Our UT-based approach to the mobility enhancement is easily applicable to different classes of soluble organic field-effect transistors by adjusting the geometrical parameters such as the height, the width, and the periodicity of the UT of an inkjet-printed insulator.

10 citations


References
More filters

Journal ArticleDOI
Abstract: Organic thin-film transistors (OTFTs) have lived to see great improvements in recent years. This review presents new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of OTFTs. The shifted focus in research from novel chemical structures to fabrication technologies that optimize morphology and structural order is underscored by chapters on vacuum-deposited and solution-processed organic semiconducting films. Finally, progress in the growing field of the n-type OTFTs is discussed in ample detail. The Figure, showing a pentacene film edge on SiO2, illustrates the morphology issue.

4,714 citations


Journal ArticleDOI
03 Feb 2000-Nature
TL;DR: It is shown that such an approach can realize much larger scales of integration (in the present case, up to 864 transistors per circuit) and operation speeds of ∼1 kHz in clocked sequential complementary circuits.
Abstract: Thin-film transistors based on molecular and polymeric organic materials have been proposed for a number of applications, such as displays and radio-frequency identification tags. The main factors motivating investigations of organic transistors are their lower cost and simpler packaging, relative to conventional inorganic electronics, and their compatibility with flexible substrates. In most digital circuitry, minimal power dissipation and stability of performance against transistor parameter variations are crucial. In silicon-based microelectronics, these are achieved through the use of complementary logic-which incorporates both p- and n-type transistors-and it is therefore reasonable to suppose that adoption of such an approach with organic semiconductors will similarly result in reduced power dissipation, improved noise margins and greater operational stability. Complementary inverters and ring oscillators have already been reported. Here we show that such an approach can realize much larger scales of integration (in the present case, up to 864 transistors per circuit) and operation speeds of approximately 1 kHz in clocked sequential complementary circuits.

1,261 citations


Journal ArticleDOI
TL;DR: This paper review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.
Abstract: In this paper we review recent progress in materials, fabrication processes, device designs, and applications related to organic thin-film transistors (OTFTs), with an emphasis on papers published during the last three years. Some earlier papers that played an important role in shaping the OTFT field are included, and a number of previously published review papers that cover that early period more completely are referenced. We also review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.

1,181 citations


Journal ArticleDOI
Abstract: A method is demonstrated by which liquid-crystalline self-organization in rigid-rod nematic conjugated polymers can be used to control the microstructure of the active semiconducting layer in solution-processed polymer thin-film transistors (TFTs). Enhanced charge carrier mobilities of 0.01–0.02 cm2/V s and good operating stability have been achieved in polyfluorene copolymer TFTs by preparing the polymer in a nematic glassy state and by aligning the polymer chains parallel to the transport direction with the help of an alignment layer. Mobility anisotropies of 5–8 for current flow parallel and perpendicular to the alignment direction have been observed that are of the same order of magnitude as optical dichroic ratios.

766 citations


Journal ArticleDOI
Abstract: We have fabricated pentacene organic thin-film transistor (OTFT) driven active matrix organic light-emitting diode (OLED) displays on flexible polyethylene terephthalete substrates These displays have 48×48 bottom-emission OLED pixels with two pentacene OTFTs used per pixel Parylene is used to isolate the OTFTs and OLEDs with good OTFT yield and uniformity

557 citations